Information Systems enjoyment has been identified as a desirable phenomenon, because it can drive various aspects of system use. In this study, we argue that it can also be a key ingredient in the formation of adverse outcomes, such as technology-related addictions, through the positive reinforcement it generates. We rely on several theoretical mechanisms and, consistent with previous studies, suggest that enjoyment can lead to presumably positive outcomes, such as high engagement. Nevertheless, it can also facilitate the development of a strong habit and reinforce it until it becomes a bad habit, that can help forming a strong pathological and maladaptive psychological dependency on the use of the IT artifact (i.e., technology addiction). We test and validate this dual effect of enjoyment, with a data set of 194 social networking website users analyzed with SEM techniques. The potential duality of MIS constructs and other implications for research and practice are discussed.